1. Field of the Invention
This invention relates to a device for detecting hidden flaws, such as delaminated areas, in a structure such as a concrete slab, and methods of using the device.
2. Discussion of the Background
Methods of and devices for detecting the presence of hidden flaws within steel reinforced suspended concrete slabs have been suggested in the prior art. The flaw to be detected is a separation, or delamination, of the layers of concrete within the slab. The delamination is caused by corrosion of the reinforcing steel within the slab. Corrosion of the steel within the suspended concrete slab is caused when moisture and chlorides make contact with the reinforcing steel. Once the steel begins to corrode, oxidation occurs and the cross-sectional dimension increases which causes areas within the concrete slab to debond and separate into two or more layers. This condition occurs in areas where there are freeze-thaw cycles as well as in areas where there is a preponderance of chlorides, either air-born or where de-icing salts are used for roadways and bridge decks. Once the oxidation and the resultant delamination starts, the rate of deterioration accelerates until a condition exists where large concrete fragments break loose and fall, or, in severe cases, a serious compromise in structural soundness of the slab occurs. Early detection, therefore, of the unseen delamination is important to keep repair costs to a minimum.
In the past, detection of delaminations in the bottom exposed surface of a suspended concrete slab, or soffit, has been to repeatedly tap the surface, usually with a hand held hammer producing the sound which has been found to occur when the slab is delaminated. This method of initially detecting the presence of delamination is regarded as a reliable means to find problem areas which are not visually apparent. Most soffits are out of reach, so a ladder or scaffolding is usually required to reach the surface.
The prior art has employed measurement of sound or vibration variables in order to ascertain changes in a mechanical element, such as a bridge, such as disclosed in U.S. Pat. No. 1,871,756 to Spath. Other prior art references have disclosed various rotary devices for obtaining acoustical data in the inspection of structures, workpieces, etc. for hidden defects, such as U.S. Pat. No. 3,714,817 and U.S. Pat. No. 3,771,354, both to Miller, and U.S. Pat. No. 4,856,334 to Shearer et al. U.S. Pat. No. 3,999,626 to Adams discloses a seismic method and apparatus for generating seismic signals which can be detected at great distances either on the surface or underground. None of the above references are concerned with defects in concrete structures, and all are drawn to relatively complex apparatus.
A method and device in the prior art disclosed for detecting delaminations is the relatively complex apparatus disclosed in U.S. Pat. No. 3,937,065 to Milberger et al. The Milberger et al apparatus is drawn to detecting delaminations beneath a surface and involves the receiving and measuring of acoustical responses with an acoustic receiving transducer, and other sophisticated components. Milberger et al's apparatus is not well adapted for detecting delaminations in areas other than the underside of floors and decks.
Another prior art delamination device is that disclosed in U.S. Pat. No. 3,361,225 to Nichols. Nichols' device comprises in combination an externally-toothed wheel, and means comprising a hand-held handle and means for pivotally mounting the wheel on the handle, for walking the wheel across a member to be tested, for causing the individual teeth of the wheel to sequentially strike the member, for producing individual sequential acoustical sounds indicative of the internal structure of the member, an abnormal acoustical sound being indicative of an abnormal internal structure. As an externally-toothed wheel, Nichols employs a disk and a single substantially coplanar set of radially outwardly-extending pegs mounted on the periphery of the disk. For extremely large panels, Nichols discloses ganging a plurality of such devices, whereby the ganged test devices may be simultaneously rolled across a panel to be tested, wherein each device detects independently of the other. Nichols discloses further the use of an electrical pickup device, such as a microphone, to detect the acoustical sounds in lieu of the use of the human ear and human judgment. The only environment disclosed for use of the Nichols' device, however, is in the detecting of abnormalities in structural elements known as honeycomb panels. A honeycomb panel is defined therein as a three-part sandwich, wherein a central core section is sandwiched between a top and bottom sheet or skin portion. The Nichols' device is intended to detect abnormalities in the bonding of the core to either the top or bottom portion. Nichols suggests nothing with regard to other structures, such as suspended concrete slabs or soffits and other generally inaccessible areas subject to delaminations.
A need thus still exists in the art for a relatively simple and inexpensive device for measuring delaminations in structures subject to such delaminations, and particularly such structures, such as suspended concrete slabs or soffits, that have previously not been tested for delaminations without great effort.